Agricultural implements can be mounted directly to agricultural tractors using a conventional three point hitch. Three point hitches have been controlled by a hitch control system which raises and lowers the hitch in response to a number of sensed parameters, including sensed draft force. Such systems can operate to lower and raise an implement while maintaining a constant load on the tractor. The implement is actually able to work at a deeper average depth as the tractor is able to operate at a higher average power with this control system. Various draft force sensing systems have been developed to provide a sensed draft force signal. Certain current production draft force sensing systems have a number of moving parts that require periodical maintenance, including removing mud and dirt accumulation and lubrication of a draft sensor plunger to prevent moisture and dirt contamination. In certain conditions, the dirt and mud accumulation actually prevents component movement which causes false draft sensing signals. Changes in tractor frame design will require new draft force sensing designs.
Some production systems have costly draft sensing pins, bending bars, and draft sensing shafts. Draft sensing pins require two instrument pins which double the cost and halve the reliability. The bending bar and draft sensing shaft systems have moving parts and require a sealed compartment and a fair amount of space. The zero load voltage for the system is set by adjusting the length of a spring steel strap that mounts over the sensor plunger and the ends of which are attached to the body of the shaft. The factory consistently has issues setting the voltage. The spring steel strap and sensor plunger produce an inconsistent voltage during spring steel strap adjustment. The current draft sensing system on 4WD tractors measures the deflection between the draft link mount straps. The components are open to the elements and exposed to mud, dirt, and debris.
It is desired to provide a draft force sensing system which can be installed within the space available in future production tractors. It is also desired to provide a draft force sensing system which is better protected from environmental contamination. It is desired to have a system which is sealed and less prone to accumulate debris.